The Kansas City man was one of the “Good Samaritan killers” who murdered Richard Drummond of Excelsior Springs, and later an Arizona couple in a 1994 crime-spree that stretched from Missouri to Mexico. Skillicorn had been on death row since his conviction in 1996.

Prior to today, Missouri hadn’t carried out an execution since October 2005.

In 2007, the state was one of several to delay executions pending the outcome of a U.S. Supreme Court case over the constitutionality of lethal injections. The high court found the method of execution constitutional in April 2008, however, and a lower court issued a similar ruling specific to Missouri a few months later.

“The jury that convicted Dennis Skillicorn determined that he deserved the most severe punishment under Missouri law, and my decision on clemency upholds the jury’s action,” Nixon said in a statement.

Skillicorn was sentenced to death for the murder of Drummond, a telephone-company supervisor who picked up Skillicorn and two other men after their car broke down in central Missouri.

Skillicorn and Allen Nicklasson continued their crime spree in Arizona, where they killed another man and his wife after the man attempted to help them with car troubles.

Nicklasson, who actually pulled the trigger in the three murders, remains on death row. The third accomplice, Tim DeGraffenreid, was a teenager when he participated in the Missouri murder and is now serving a life sentence.